1. Technical Field
The present invention relates to an oscillator, an electronic device and a moving object.
2. Related Art
A quartz crystal oscillator used for a reference frequency signal source such as a communication device or a measurement device is required to have a stable output frequency with a high accuracy with respect to a temperature change. In general, An Oven Controlled Crystal Oscillator (OCXO) which can obtain extremely high frequency stability, among the quartz crystal oscillators is known (refer to JP-A-2010-183228). The OCXO is configured by a quartz crystal resonator contained in a constant temperature oven which is controlled at a constant temperature, and in order to realize the extremely high frequency stability, it is important to make temperature control deviation of the constant temperature oven as small as possible with respect to an ambient temperature change.
FIG. 16A is a view illustrating an example of frequency-temperature characteristics in a case where a temperature control of the constant temperature oven is not performed in the OCXO using an SC-cut quartz crystal resonator, and FIGS. 16B and 16C are views where a portion surrounded by a dashed line is enlarged. By maintaining the temperature inside the constant temperature oven at approximately 80° C., the OCXO can output a stable frequency with a small deviation although the ambient temperature changes. The accuracy of the constant temperature oven is different depending on products, but for example, in a case where the ambient temperature changes from −40° C. to 80° C., and the constant temperature oven changes by ±2° C. from 80° C., the frequency deviation is approximately 20 ppb (hatched portion in FIG. 16B). On the other hand, in a case where the temperature inside the constant temperature oven is set to 80° C., but the temperature inside the constant temperature oven is actually 82° C. shifted by 2° C. to the high temperature side, and the constant temperature oven changes by ±2° C. from 82° C., a frequency of the OCXO has secondary temperature characteristics, and the frequency deviation thereof becomes 40 ppb (hatched portion in FIG. 16C).
In addition, an oscillation circuit and a frequency adjustment circuit also have the temperature characteristics, and it is common that the temperature characteristics are given in such a manner that the frequency of the OCXO decreases linearly with respect to an increase in temperature. Thus, by the setting temperature shifting of the constant temperature oven or the temperature characteristics of a circuit, the frequency-temperature characteristics of the OCXO which should be originally flat have a primary component or a secondary component. For this reason, in the OCXO of the related art, there is a problem that it is difficult to satisfy requirements of the extremely high frequency stability.